Effects of Scutellaria baicalensis Georgi on Macrophage-Hepatocyte Interaction Through Cytokines Related to Growth Control of Murine Hepatocytes

Abstract

The aim of this study is to elucidate the effects of Scutellaria baicalensis Georgi (SbG) extract and its constituents on macrophage-hepatocyte interaction in primary cultures. By using trans-well primary Kupffer cell culture or conditioned medium (CM) from murine macrophage RAW264.7 cell line (RAW cells), effects of SbG on hepatocyte growth were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and trypan blue exclusion assay. Cytokine production, antibody-neutralization studies, and molecular mechanisms of transforming growth factor (TGF)-β1 gene expression were elucidated on SbG-treated RAW264.7 cells. In addition, recombinant human TGF-β1 (r-human TGF-β1) was added to elucidate the mechanisms of SbG effects on cultured hepatocytes. Immunohistochemistry using anti-NF-κB antibody was used to determine the possible signal transduction pathways in primary hepatocyte culture. The results showed that SbG stimulated the proliferation of cultured hepatocytes, possibly through NF-κB, but not of Toll-like receptor 4 activation; whereas SbG-RAW-CM and SbG in trans-well significantly suppressed the proliferation of hepatocytes. Antibody-neutralization studies revealed that TGF-β1 was the main antimitotic cytokine in SbG-treated RAW cells CM. The growth stimulation effect of SbG on cultured hepatocytes was inhibited by exogenous administration of r-human TGF-β1. Furthermore, SbG induced NF-κB translocation into the nuclei of cultured cells. In the RAW264.7 line, SbG and baicalin stimulated TGF-β1 gene expression via NF-κB and protein kinase C activation. We conclude that SbG stimulates hepatocyte growth via activation of the NF-κB pathway and induces TGF-β1 gene expression through the Kupffer cell–hepatocyte interaction, which subsequently results in the inhibition of SbG-stimulated hepatocyte growth.